Direct Observation of Conducting Nanofilaments in Graphene-Oxide-Resistive Switching Memory

Determining the presence of conducting filaments in resistive random access memory with nanoscale thin films is vital to unraveling resistive switching mechanisms. Bistable resistive switching within graphene-oxide (GO)-based resistive memory devices, recently developed by many research groups, has been generally explained by the formation and rupture of conducting filaments induced by the diffusion of metal or oxygen ions. Using a low-voltage spherical aberration-corrected transmission electron microscopy (TEM), we directly observe metallic nanofilaments formed at the amorphous top interface layer with the application of external voltages in an Al/GO/Al memory system. Atomic-resolution TEM images acquired at an acceleration voltage of 80 kV clearly show that the conducting nanofilaments are composed of nanosized aluminum crystalline within the amorphous top interface layer after applying a negative bias (ON state). Simultaneously, we observe the change in the crystallinity of GO films by the back-diffusion of oxygen ions. The oxygen-deficient regions are clearly confirmed by energy-filtered TEM oxygen elemental mapping. This work could provide strong evidence to confirm the resistive switching mechanism previously suggested by our group.